<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width,initial-scale=1">
    <title>Title</title>
    <link rel="stylesheet" href="./bootstrap.min.css" crossorigin="anonymous">
  <style>
    .loginRow{
      width: 100%;
      color: #fff;
      text-align: center;
      margin: 0 auto;
      background-color: #2b542c;
    }
    @media screen and (min-width: 601px) {
      .loginRow{
        width: 500px;
        margin: 0 auto;
        border-radius: 10px;
      }
    }

  </style>
</head>
<body>
    <div class="loginRow">
      <h1>登录框</h1>
    </div>
</body>
</html>